This invention relates to magnetoresistance effect elements using a multilayered magnetic thin film with high magnetoresistance effect, and particularly to magnetoresistance effect elements, magnetic heads and magnetic storage apparatus for achieving high-density recording on a magnetic recording medium on which narrow tracks are formed.
An investigation is now being made of magnetic heads using the magnetoresistance effect for high density-magnetic recording. At present, an alloy film of Ni-20 at % Fe is used for the magnetoresistance effect material. However, a magnetoresistance effect element using the Ni-20 at % Fe alloy film often causes noise such as Barkhausen noise, and thus other magnetoresistance effect materials are also under investigation.
On the other hand, recently Suezawa, et al. have reported a magnetoresistance effect film which utilizes the ferromagnetic spin-dependent tunneling phenomenon and which detects magnetic flux from the electrical resistance change of a multilayered film having a pair of magnetic layers divided by an insulating layer, as is disclose in Proceedings of the International Symposium on Physics of Magnetic Materials, Apr. 8-11, 1987, pp. 303-306. This report has introduced a multilayered structure of a Ni/NiO/Co junction and multilayered films of Al/Al.sub.2 O.sub.3 /Ni, Co--Al/Al.sub.2 O.sub.3 /Ni exhibiting the ferromagnetic spin-dependent tunneling effect. However, in either case, the junction area between the pair of magnetic layers is as wide as about 1 mm.sup.2, and the relative resistivity change, .DELTA..rho./.rho. is as small as about 1% at room temperature. In addition, since the element structure shown in this example is not capable of sensing a small magnetic flux change, it is impossible to precisely detect the change of magnetic flux leaking from a magnetic recording medium recorded at a high density.
In the prior art, a Ni/NiO/Co multilayer, for example, has an Ni layer and a Co layer of a rectangular shape made perpendicular to each other to allow all current to pass the NiO layer to effectively detect the resistance change due to the ferromagnetic spin-dependent tunneling effect. However, when used for a magnetic head, the intersection of the ferromagnetic Ni layer and Co layer will be insufficient to precisely detect the magnetic field in a narrow region because the longitudinal direction of either magnetic layer is parallel to the surface of the magnetic recording medium. In other words, the magnetic flux change associated with the signal recorded in a narrow track cannot be detected with a high sensitivity.
Moreover, the ferromagnetic spin-dependent tunneling effect of an Fe/C/Fe multilayer has been reported by J. C. Slonczewski in Phys. Rev. Vol. B39, pp. 6995, 1989, "Conductance and Exchange Coupling of Two Ferromagnets Separated by a Tunneling Barrier".
In the application of the ferromagnetic tunneling film to the magnetic heads, the ferromagnetic tunneling film is required not to deteriorate in its characteristics in the course of the magnetic head producing process. The magnetic head producing process often includes a heating process. However, when the Fe/C/Fe multilayer film is heated to 300.degree. C. or above, carbon C is diffused into the Fe layer, thus deteriorating the characteristics. Also, when the intermediate layer is made of an oxide such as NiO or Al.sub.2 O.sub.3, the interface energy increases in the interface between the magnetic layers and the intermediate layer. The increase of the interface energy will act to decrease the number of atoms in the interface, thus causing defects such as vacancies in the intermediate layer and magnetic layer, so that the soft magnetic characteristics may be deteriorated as described by Nakatani, et al. in J. Appl. Phys., Vol. 66, pp. 4338, 1989, "Changes in Soft Magnetic Properties of Fe Multilayered Films due to Lattice Mismatches between Fe and Intermediate Layers".
Moreover, an Fe/Cr multilayered film has recently been reported, of which the relative resistivity change is about 50% as described in Physical Review Letters, Vol. 61, No. 21, pp. 2472 to 2475, 1988.
In the magnetoresistance effect element having such a multilayer structure as the Fe/Cr multilayered film, the electrical resistance is changed by the magnetic field when electrons are moved from a magnetic layer to another magnetic layer, or passed through a non-magnetic intermediate layer. At this time, the current is flowed in the film-thickness direction. However, the film thickness of the magnetic film is several hundreds of nm or below and the element resistance is low. Thus, the rate of resistance change is high, but the amount of resistance change is small. When this film is applied to an actual magnetic sensor or magnetic head, the output is small.
Also, in the magnetic disk apparatus, magnetic heads are used for writing and reading information on and from a magnetic recording medium, and in this case the electromagnetic induction-type ring head, for example, is widely used for the magnetic head for writing and reading. In a rigid-type magnetic disk apparatus for a computer, an induction current is flowed in the magnetic head which is floated with a very small gap from the surface of a disk-like magnetic recording medium rotating at a high speed, so that the magnetic field generated at the tip of the magnetic head can enable recording on the magnetic recording medium. As the recording density is improved so that the recorded bits are small, it has been demanded to use a magnetic head having a high writing and reading efficiency. In the prior art, the same ring head has been used for writing and reading, but no dual elements are used for an inductive-write and magnetoresistant-read dual-element magnetic head for improving their functional efficiency. An example of this dual-element magnetic head is disclosed in Japanese Patent laid-open Gazette No. JP-A-51-44917. For the dual-element magnetic head, it is desired to use elements having a particularly high-sensitivity reading function, in which case the magnetic detecting element using the magnetoresistance effect (Japanese Patent Publication No. JP-B-53-17404) and the magnetic detecting element using the magnetosensitive transistor (Japanese Patent Laid-open Gazette No. JP-A-57-177573) are proposed. However, these elements do not have enough magnetic detection sensitivity for high-density magnetic recording over 100 Mb/in.sup.2.